The distribution and frequency of the type II microtrichs in some gammaridean amphipods

Abstract

The distribution and frequency of the type II microtrichs was determined with the aid of the scanning electron microscope in several gammarid species from different habitats in the marine environment. The type II microtrichs are recessed in shallow cuticular depressions on the tergum and occur in dorsal and/or lateral groups on the somites and the telson. The frequency of these microtrichs varies directly with the body length for any one species, and in the different gammaridean taxa studied. The commensal and supralittoral gammarids have none or very small numbers. The average numbers per somite are higher in the intertidal species of Gammarus, then increase in the subtidal Calliopius, and reach very large numbers in the benthic Anonyx and Halirages. On the average, the microtrichs on the pleon outnumber those on the peraeon somites. Large-sized Halirages and Anonyx have very large numbers on pleon somite 11. The possible significance of these differences is discussed.